In recent years, in the field of electrophotographic printing which is applied to high-speed laser/LED printers, copy machines and multifunctional printers, the specifics of printing machines and toners are changing due to the growing demand for high image quality, speeding up of printing, and energy-saving. With the changes, in the image-forming process in which electric-charging, exposure, image development, transfer, fixing, cleaning and neutralization are repeated, more specifically, in the toner removing process which removes the toner remained on a photoreceptor after transferring toner image, cleaning accuracy becomes more important than ever before.
Especially, in the field of high-speed printing, since the cycle speed of the image-forming process is high, toner is easily slipped through, and thus it is required to certainly remove the remaining toner in a short time. However, since the toner is used for high image quality printing, the processed toner having fine grains is used. Therefore, improvement of durability is required for preventing the toner from slipping through. Furthermore, in high-speed printing, the temperature increases greatly when continuous printing is performed, and in the printing for energy-saving strategy, in order to shorten the start-up time or restart-up time after sleep mode, stability of cleaning performance capable of responding to variations of external temperature is also required.
Until now, in order to reduce the temperature dependency of cleaning performance while keeping an ultralow rebound resilience, a polyurethane elastomer using 1,9-nonane diol, methyl-1,8-octane diol/adipic acid or sebacic acid was used as a polyester polyol wherein Mn=500 to 5000 and ester group concentration=6 to 8 mmol/g. However, in the said composition ratio, the permanent elongation becomes large, and there is a problem in that the long-term durability of the cleaning blade contacting a photoreceptor at the flexural state is inferior (refer to Patent Documents 1 and 2).
Furthermore, a polyurethane elastomer using a polyester diol having an ester group concentration of 6 to 8 mmol/g and an alkyl side chain concentration of 2 to 4 mmol has been proposed. However, when a polyester diol having an alkyl side chain concentration of 2 mmol or more is used, the tensile strength at break and the tear strength of the polyurethane elastomer decrease significantly, and a trouble chipping very small pieces of polyurethane elastomer is caused when the cleaning blade is used for a long time (refer to Patent Document 3).    Patent Document 1: Japanese Examined Patent Application Publication No.    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2004-292809,    Patent Document 3: Japanese Examined Patent Application Publication No. 3877065